Transocean Ltd., the Swiss company that owned and operated the Deepwater Horizon oil rig, says the Gulf of Mexico oil spill that occurred last year is the result of successive decisions made by well owner BP. BP calls it "an advocacy piece" to support Transocean's "litigation strategy."

Wisner Properties Field Inspector Forrest Travirca walks in an area of dead marsh grass that was impacted by oil from the BP oil spill in Port Fourchon, La., April 20, 2011. Lengthy legal battles lay ahead. BP filed a lawsuit alleging negligence by the maker of the device that failed to stop the spill, while the manufacturer of the blowout preventer and rig owner filed their own claims.

Chicago — Transocean Ltd., the Swiss company that owned and operated the Deepwater Horizon oil rig, says the Gulf of Mexico oil spill that occurred last year is the result of successive decisions made by well owner BP that compromised the integrity of the well, resulting in 11 deaths and the discharge of 205 million gallons of oil into ocean waters over three months.

The company released an 854-page report in late June that follows a narrative consistent in blaming BP for “a succession of interrelated well design, construction and temporary abandonment decisions” that led to the well’s failure on April 20, 2010.

The company charges that BP “retained full authority over drilling operations, casing and cementing, and temporary abandonment procedures, including approval of all work to be performed by contractors and subcontractors,” and proceeds to show how that authority was misused with disastrous results.

• The cement BP used to isolate the reservoir to prevent hydrocarbons from entering the well was “of minimal quality, left little margin for error and was not tested adequately before or after the cementing operation.” A hydrocarbon is a compound consisting of hydrogen and carbon, the high flow of pressure of which is blamed for making it difficult for the blowout preventer to seal the well properly.

• BP and Halliburton, the cementing contractor in the operation, did not perform tests to determine the stability of the cement. The report also says BP filed to use risk assessment tests approved by the Mineral Management Service [MMS], the now-dismantled federal agency charged with regulating drilling procedures and operations, in its effort to temporarily seal the well that would allow it to return to the site at a later time.

• BP failed to communicate properly with the drill crew regarding the instability of the cement mixture and the lack of testing involved in the process.

Despite its continual criticisms of BP, Transocean says the report does not represent its legal position “nor does it attempt to assign legal responsibility or fault.” The company describes the report as the result of an internal investigation by a team of experts.

The report is the latest in a series from several parties, including BP, involved in the spill. In each case, an attempt is made to create a factual record, which can be used as both a shield and as authoritative evidence in the numerous lawsuits that are currently underway and are expected to last years.

In January, the National Oil Commission released a 398-page report that spread blame relatively equally among BP, Transocean, and Halliburton, the three leading players involved in the disaster. The report also recommended removal of the $75 million liability cap to cover economic damages, giving the government flexibility to impose fines that are expected to be in the billions of dollars.

In a statement, BP said the Transocean report “fails to acknowledge the significance of Transocean’s role in the event” and said “on its face, it appears to be an advocacy piece, in which Transocean has cherry-picked the facts in support of its litigation strategy.” BP adds that the report needs to be read in the context of the presidential commission report and another by the US Coast Guard, both of which criticize Transocean for safety issues related to the disaster.

Halliburton also responded to the report, saying in a statement that, “deepwater operations are inherently complex and a number of contractors are involved which routinely make recommendations to a single point of contact, the well owner,” which is BP.

Local, state, and federal officials involved in the disaster are saying the report should be treated with a degree of suspicion considering the ongoing litigation and possible liability suits to come.

Chris Roberts, a council member of Jefferson Parish, an area in coastal Louisiana that suffered economic loss as a result of the oil spill, told the Associated Press that “obviously, there’s a monetary gain or loss depending upon what [Transocean] show their findings to be.”

When BP released its own report in September 2010 laying blame to both Transocean and Halliburton, both companies complained it was an attempt by the company to deflect responsibility. Transocean called the BP report “self-serving” and an attempt to conceal what it described as “BP’s fatally flawed well design.”